1. Technical Field
The present disclosure generally relates to electronic circuits and, more specifically, to circuits comprising elements for generating one or several periodic signals implementing a method for spreading the spectrum of the radiation of the periodic signal(s). The present disclosure more specifically relates to the estimating of the parameters of a method for spreading the spectrum of periodic signals.
2. Description of the Related Art
Synchronous electronic circuits are generally clocked by at least one clock signal. In operation, such circuits may emit an electromagnetic radiation having a spectrum which comprises a main line at the frequency of the clock signal and secondary lines at the harmonics. The spectral line at the frequency of the clock signal concentrates most of the radiated power. This may result in electromagnetic interferences with adjacent electronic circuits. Such is the case, for example, for electronic circuits comprising high-speed series connections which may emit a radiation disturbing adjacent circuits.
To decrease the power of the main line of the radiation emitted by a synchronous electronic circuit, a possibility is to slightly vary the frequency of the clock signal along time to spread the spectrum of the emitted electromagnetic radiation. Such a method for spreading the spectrum of the clock signal, better known as Spread Spectrum Clocking, will be called SSC method hereafter.
An SSC method generally comprises carrying out a modulation of the frequency of the clock signal or SSC modulation. Most often, the clock frequency is modulated by a periodic triangular signal defined by two parameters: modulation period Tmod and modulation ratio Rmod. Ratio Rmod is generally defined as being the ratio of half the difference between the maximum clock frequency and the minimum clock frequency to a reference frequency, for example, the average frequency of the clock signal.
A difficulty is to estimate the parameters of an SSC method implemented by an electronic circuit. Indeed, while it is relatively easy to acknowledge the absence of implementation of an SSC by spectral analysis of the radiation emitted by an electronic circuit, it is more difficult to determine the parameters of the SSC method based on the analysis of the clock signal of the circuit to determine whether the SSC method actually implemented corresponds to the expected SSC method. This can generally only be performed by means of relatively complex dedicated tools, the use of which, in terms of cost and duration, cannot be envisaged to test electronic circuits manufactured at an industrial scale.